This invention relates generally to semiconductor packaging and specifically to an improved BGA package, and to a method for fabricating the BGA package.
One type of semiconductor package is referred to as a BGA package. BGA packages were developed to provide a higher lead count, and a smaller foot print, than conventional plastic or ceramic semiconductor packages. A BGA package includes an array of external ball contacts, such as solder balls, that permit the package to be surface mounted to a printed circuit board (PCB) or other electronic component. Some BGA packages have a foot print that is about the size of the die contained in the package. These BGA packages are also known as chip scale packages.
BGA packages typically include a substrate which comprises a reinforced polymer laminate material, such as bismaleimide triazine (BT), or a polyimide resin. Patterns of metal conductors formed on the substrate form the internal signal traces for the package. The conductors can include wire bonding pads for wire bonding bond wires to the die, and ball bonding pads for attaching external ball contacts, such as solder balls. An encapsulating resin, such as a Novoloc based epoxy, can also be molded onto the substrate to encapsulate the die and bond wires.
Fabrication processes for BGA packages differ from the fabrication processes for conventional plastic packages. In particular, for fabricating conventional plastic packages metal lead frames are employed. The lead frames include patterns of lead fingers which form the internal signal traces and external leads of the package. Since equipment and procedures have been developed for packaging dice using metal lead frames, it would be advantageous to adapt metal lead frames to the fabrication of BGA packages.
U.S. Pat. No. 5,677,566 to King et al, discloses a BGA package fabricated using a metal lead frame. This package employs a leads over chip (LOC) lead frame having lead fingers to which the die is wire bonded. The lead fingers include ball bonding pads which are aligned with openings in an encapsulating material. The openings allow ball contacts, such as solder balls, to be bonded to the ball bonding pads on the lead fingers.
The present invention is also directed to a BGA package in which a metal lead frame can be employed to fabricate the package. The lead frame includes lead fingers configured to provide an increased density, or xe2x80x9cpacking fractionxe2x80x9d for the ball contacts. This permits the package to be fabricated with a dense area array of ball contacts. In addition, the lead frame can be configured for packaging different sizes of dice, while at the same time, the size and external configuration of the package and ball contacts can be standardized. In a second embodiment of the invention the lead frame is replaced by a polymer tape and the die is flip chip mounted to beam leads on the tape.
In accordance with the present invention, an improved BGA package, and a method for fabricating the package are provided. The BGA package, broadly stated, comprises: a semiconductor die; internal conductors in electrical communication with the die; external ball contacts attached to the conductors; and an encapsulating resin encapsulating the die and conductors. The encapsulating resin includes openings for locating and electrically insulating the ball contacts on the conductors. The openings also provide access to the conductors for testing the die prior to attachment of the ball contacts.
In a first embodiment of the BGA package, the conductors are formed by lead fingers of a lead frame. A polymer tape electrically insulates the lead fingers, and supports the die for wire bonding to the lead fingers. The lead fingers include wire bonding pads on a first side thereof, for wire bonding to bond pads on the die. The lead fingers also include ball bonding pads on an opposing second side thereof, for attaching the external ball contacts. The lead fingers and ball bonding pads on the lead fingers are formed in a configuration that permits the ball contacts to be arranged in a dense area array, such as a ball grid array. In addition, bond wires in the package are protected, and the package can be similar in size to a conventional thin small outline package (TSOP) but with a dense array of ball contacts rather than wire leads.
A method for fabricating the first embodiment BGA package comprises the steps of: providing a semiconductor die; providing a lead frame including lead fingers having wire bonding pads and ball bonding pads in a dense area array; placing a polymer tape on the lead fingers; back bonding the die to the polymer tape by forming an adhesive layer therebetween; wire bonding the die to the wire bonding pads; encapsulating the die and lead fingers in an encapsulating resin having openings aligned with the ball bonding pads; and attaching ball contacts to the ball bonding pads. In general each of these steps can be performed using equipment identical or similar to equipment used to fabricate conventional plastic semiconductor packages using lead frames.
In a second embodiment of the BGA package, the die is flip chip mounted to conductors contained on a polymer substrate adhesively bonded to a face of the die. The conductors include beam leads that are bonded to the bond pads on the die, and ball bonding pads for attaching the ball contacts. The polymer substrate includes an elongated opening aligned with the beam leads which provides access for a bonding tool. The polymer substrate also includes openings aligned with the ball bonding pads, which provide access for attaching the ball contacts to the ball bonding pads, and for making electrical connections for testing the die prior to attachment of the ball contacts. As with the first embodiment BGA package, the ball bonding pads are arranged in a dense area array.
A method for fabricating the second embodiment BGA package comprises the steps of: providing a semiconductor die having a face with bond pads thereon; providing a polymer substrate having conductors with beam leads for bonding to the bond pads and ball bonding pads for attaching ball contacts; adhesively bonding the polymer substrate to the face of the die; flip chip bonding the bond pads on the die to the beam leads on the conductors; encapsulating the die and conductors in an encapsulating resin having openings aligned with the ball bonding pads; and attaching the ball contacts to the ball bonding pads.